Carbon nanotubes in various forms have been disclosed. However, conventional carbon nanotubes, in the form of fibers or fibrils, are “clumped” together, making them less than ideal or even useful to their full potential, due to the entangled nature of the fibers. The present invention provides a method for separating these nanotubes into individual fibers and fibrils, and these separated “discrete” (un-entangled) carbon nanotube fibers are useful in many applications, including reinforcement of other materials. In an embodiment of the present invention, discrete carbon nanotube fibers are used in urethane polymers and prepolymers, especially for making rigid and flexible foams, adhesives, sealants, coatings, and elastomers.